1. Field of the Invention
The present invention relates to the field of anti-cancer therapy, and, more particularly to small molecule inhibitors of Ire 1 endonuclease activity.
2. Related Art
Presented below is background information on certain aspects of the present invention as they may relate to technical features referred to in the detailed description, but not necessarily described in detail. That is, individual parts or methods used in the present invention may be described in greater detail in the materials discussed below, which materials may provide further guidance to those skilled in the art for making or using certain aspects of the present invention as claimed. The discussion below should not be construed as an admission as to the relevance of the information to any claims herein or the prior art effect of the material described.
Multiple myeloma (MM) is a B cell neoplasm associated with unregulated/uncontrolled differentiation and proliferation of mature B cells to plasma cells. Despite significant therapeutic advances in recent years, MM remains an incurable disease in most patients (Raab M S, Podar K, Breitkreutz I, Richardson P G, Anderson K C. Multiple myeloma. Lancet. 2009; 374:324-339). Due to high production of secreted antibodies, MM cells display chronic ER stress, and their survival is dependent upon the adaptive Ire1-XBP1 branch of the unfolded protein response (UPR) pathway (Davenport E L, Moore H E, Dunlop A S, et al. Heat shock protein inhibition is associated with activation of the unfolded protein response pathway in myeloma plasma cells. Blood. 2007; 110(7):2641-2649). Investigators have shown that perturbing the UPR with proteosome inhibitors can sensitize MM cells to apoptosis (Lee A H, Iwakoshi N N, Anderson K C, Glimcher L H. Proteasome inhibitors disrupt the unfolded protein response in myeloma cells. Proc Natl Acad Sci USA. 2003; 100:9946-9951). The FDA has approved the proteasome inhibitor bortezomib as the first example of a UPR modulating chemotherapy for the treatment of MM (Field-Smith A, Morgan G J, Davies F E. Bortezomib (Velcadetrade mark) in the Treatment of Multiple Myeloma. Ther Clin Risk Manag. 2006; 2:271-279).
Recent in vitro Ire1 kinase and RNase assays have yielded insight into determining the mechanism of Ire1 activation (Nock S, Gonzalez T N, Sidrauski C, Niwa M, Walter P. Purification and activity assays of the catalytic domains of the kinase/endoribonuclease Ire1p from Saccharomyces cerevisiae. Methods Enzymol. 2001; 342:3-10; Dong B H, Niwa M, Walter P, Silverman R H. Basis for regulated RNA cleavage by functional analysis of RNase L and Ire1p. Rna-a Publication of the Rna Society. 2001; 7:361-373). Mutant Ire1 proteins with amino acid substitutions at conserved positions in the kinase domain identified nucleotide binding and kinase-domain phosphorylation as necessary for Ire1 RNase activation (Tirasophon W, Welihinda A A, Kaufman R J. A stress response pathway from the endoplasmic reticulum to the nucleus requires a novel bifunctional protein kinase/endoribonuclease (Ire1p) in mammalian cells. Genes Dev. 1998; 12:1812-1824; Korennykh A V, Egea P F, Korostelev A A, et al. The unfolded protein response signals through high-order assembly of Ire1. Nature. 2009; 457:687-693; Han D, Lerner A G, Vande Walle L, et al. IRE1alpha kinase activation modes control alternate endoribonuclease outputs to determine divergent cell fates. Cell. 2009; 138:562-575). However, a report found that an ATP competitive inhibitor, 1NM-PP1, could activate Ire1 that contained a mutation in the ATP binding site. In this context, kinase activity was not required for Ire1 function, suggesting that Ire1 activity may be modulated through an allosteric mechanism (Papa F R, Zhang C, Shokat K, Walter P. Bypassing a kinase activity with an ATP-competitive drug. Science. 2003; 302:1533-1537.) The crystal structure of the cytosolic portion of activated yeast Ire1 revealed a back-to-back configuration of the kinase domain within the Ire1 dimer (Lee K, Dey M, Neculai D, Cao C, Dever T, Sicheri F. Structure of the dual enzyme Ire1 reveals the basis for catalysis and regulation in nonconventional RNA splicing. Cell. 2008; 132:89-100). This structure supported a model in which dimerization (or oligermization) of Ire1 juxtaposes kinase domains which facilitates trans-autophosphorylation of the protein, resulting in a competent nuclease pocket and enhanced Rnase activity (Korennykh A V, Egea P F, Korostelev A A, et al. The unfolded protein response signals through high-order assembly of Ire1. Nature. 2009; 457:687-693; Han D, Lerner A G, Vande Waite L, et al. IRE1alpha kinase activation modes control alternate endoribonuclease outputs to determine divergent cell fates. Cell. 2009; 138:562-575).
More recently, the flavanoid quercetin was shown to activate Ire1 through a newly described ligand-binding pocket along the Ire1 dimer interface (Wiseman R, Zhang Y, Lee K, et al. Flavonol activation defines an unanticipated ligand-binding site in the kinase-RNase domain of Ire1. Mol Cell. 2010; 38:291-304). These data suggest the pharmacologic potential for multiple ligands to selectively modulate either Ire1 kinase or RNase activity.